1. Field of the Invention
This invention deals relates to data communication networks. More particularly, the invention relates to a method and system for optimizing data line/link occupation in a multipriority data traffic environment by using data multiplexing techniques of asynchronously transmitted fixed or variable length data packets.
2. Background Information
Modern digital networks are made to (1) operate in a multimedia environment for transporting different kinds of digitally encoded data including voice, images, video signals etc. . . , and (2) enable worldwide coverage while ensuring compliance with a number of requirements specific to each kind of traffics. For instance, while so-called non-real time information can be delivered to the corresponding end-user with minor time constraint restrictions, real-time type of information must be delivered to end-user with predefined limited time delay restrictions.
World-wide coverage is achieved by interconnecting different types of networks including network nodes (i.e., access nodes and transit nodes) connected to each other through high speed lines herein also referred to as links. Such a composite network is represented in FIG. 1. The users get access to the network through ports located in the access nodes. The users' data are processed by an access agent running in the port. The functions of the access agent are two-fold: First interpret the user's protocol, and second set the path and route the data through the network.
Different techniques have been developed for organizing the digitally encoded data transport. These include packet switching techniques whereby the digitized data are arranged into so-called packets. The packets may either be of fixed length, like in the so-called Asynchronous Transfer Mode (ATM), or be of variable length (VL) nature.
A modern international network may be rather complex, include leased lines and look like the network of FIG. 2.
In addition to leased lines, this network would support Frame Relay and ATM networks. The network offers the possibility of carrying native Asynchronous Transfer Mode (ATM) traffic as well as Variable Length (VL) traffic, which VL traffic may include both user's traffic and control traffic. A fundamental difference between both VL traffics is that while user's traffic needs be vehiculated along a given path from a source end user to a destination end user without affecting the network, control traffic should be addressed to (a) specific node (s), be decoded therein and control the very network architecture and operation. It should also be noted that whatever be the type of traffic, data are provided to the network at random.
The above description of networks helps visioning complex modern network transmission facilities. The description also helps understanding that the system should be optimized from a cost efficiency standpoint. Accordingly, the present invention shall focus on link operation efficiency, and more particularly optimizing link bandwidth occupation.
Let's first recall that links available in the US include so-called T1 operating at 1.544 Mbps and T3 at 44.736 Mbps, while in Europe one may find the E1 at 2.048 Mbps and E3 at 34.368 Mbps.
Now, let's assume a network service provider requires either an access link to a network or a link between two nodes at medium rate, say between 2 and 10 Mbps. The obvious solution should lead to selecting a T3/E3 link. However, such selection would not fit from a cost/efficiency standpoint, bearing in mind the presently practiced tariffs. For example, these tariffs in 1995 are in France (in K$/month) as indicated hereunder:
______________________________________ 50 Km 250 Km 500 Km ______________________________________ E1 = 2 10 14 E3 = 50 150 170 ______________________________________
Accordingly, selecting higher than actually required rates would be prohibitive and one should find a solution for intermediate rates at affordable prices, i.e., optimize bandwidth occupation. A first solution that comes to a network designer's mind involves using multiplexing techniques, that is, for instance, cover a 10 Mbps bandwidth requirement with five multiplexed E1 in Europe or seven T1 in the US, or multiplex equivalent virtual channels within a high speed link.
Both hardware and software alternatives may be designed. However, hardware solution would suffer the drawback of both high development cost and time to market. Obviously, one would prefer keeping the already available network hardware architectures (e.g., node architectures) and shoot for software modification.
On the other hand any software implementation of such a multiplexing system should fit with the specific traffic requirements, including quality of service traffic granularity, etc . . . , in any variable and/or fixed length packet switching network, while requiring minimal development cost for implementation in already existing network architectures.